(a) Field of the Invention
The present invention relates to a complex metal oxide, and a method of preparing polyester using the same. More particularly, the present invention relates to a complex metal oxide including three kinds of metal and having a stabilized structure to be capable of being used as a catalyst for polyester polymerization, and a method of preparing polyester using the same.
This application claims the benefit of Korean Patent Application No. 2012-0038477 filed in the Korean Intellectual Property Office on Apr. 13, 2012, the entire contents of which are incorporated herein by reference.
(b) Description of the Related Art
Polyester has been applied to various fields, for example, a beverage filling container, a medical packaging material, a sheet, a film, and a car molded product which have been applied from the related art, due to excellent mechanical properties and chemical properties. Representative example thereof includes polyethylene terephthalate. The polyethylene terephthalate has been widely used due to excellent physical and chemical properties, dimensional stability, and the like, and is mainly prepared by using an antimony (Sb)-based catalyst.
However, in the case of products manufactured by the antimony-based catalyst, a large amount of antimony needs to be used in polymerization process, and the antimony itself has toxicity, such that at the time of using the products for a long time, the antimony may leak and may be introduced in vivo, causing deterioration of fetal growth, diseases such as carcinogenicity, and the like, and leading to environmental problems (Appl. Polym. Sci. 2004, 92, 1887). In accordance with the recent research results, it is known that even in a drinking water bottle, and a food packaging material manufactured by using the antimony catalyst, a large amount of antimony causing toxicity in vivo is detected (J Environ. Monit. 2006, 8, 288). Accordingly, in some advanced countries, regulation or ban on the use of the antimony-based catalyst has gradually proceeded, and an environmentally friendly catalyst capable of substituting for a toxicity-inducing metal such as antimony has been developed.
Regarding this, methods of using a metal compound capable of substituting for a highly toxic antimony-based catalyst, and having a low toxicity in vivo, and known as being environmentally friendly, as a catalyst for polyester polymerization, have been suggested.
For example, International Publication Patent No. WO95/018839 discloses a catalyst preparing polyester and copolyester by using TiO2/SiO2 or TiO2/ZrO2 oxide coprecipitate. In addition, Japanese Patent Laid-Open Publication No. 2003-40991 suggested a method of polymerizing polyester by using a complex oxide such as TiO2/Al2O3, TiO2/SiO2 or TiO2/ZrO2 as a catalyst.
However, the catalysts used in the above-described methods have a limitation in that a small amount of phosphorus (P) should be used as an additive serving as a thermal stabilizer and an antioxidant used in the polymerization process of the polyester, such that during the melting and molding process, it is easy to cause pyrolysis, oxidation degradation and a yellowing problem of polyester. Therefore, at the time of manufacturing a film and a drinking water container using the polyethylene terephthalate polymerized by using the existing complex oxide catalyst, since the yellowing problem occurs, the product has a darkened brightness, which is not appropriate for commercialization. In addition, since activity of the catalyst itself is not controllable in the polycondensation, polymer having a large distribution of molecular weight is prepared, such that it is difficult to obtain polyester having a desired viscosity in a solid phase polymerization.
Therefore, development of a catalyst capable of being environmentally friendly and stabilized with phosphorus, and having few problems such as pyrolysis, oxidation degradation, and yellowing problem at the time of utilizing molded products manufactured by using a resin obtained by polyester polymerization using the catalyst, has been still demanded.